It is well established that reinforcing effects of abused drugs play a key role in the development and maintenance of drug addictions. Animal models have been successfully developed and used to study these reinforcing effects. The most adequate procedures are based on drug administration made contingent upon animal subject's behavioral response(s). Available drug self-administration procedures differ with regard to numerous variables. Since 1988, our research laboratories at Pavlov Medical University have been working with the intravenous self-administration (IVSA) procedure in drug- and experimentally naive mice. Great progress has been made and a large body of preliminary data is available. Overall, the IVSA model is a very fast, fairly inexpensive procedure that is suitable for screening the new compounds for abuse liability and for behavioral genetics studies. This project is focused on demonstrating that the IVSA is an adequate experimental model for assessing the primary reinforcing effects of drugs that is sensitive to various pharmacological, environmental and genetic influences that are known to affect drug self-administration in conventional study protocols. The specific aims of the proposed project are: 1) to characterize the intravenous drug self-administration in drug- and experimentally naive animals (IVSA protocol) under different schedules of reinforcement; 2) to reproduce all typical phases of conventional drug self-administration using the IVSA protocol (acquisition - extinction - reinstatement); 3) to evaluate impact of social (social hierarchy status) and genetic (different strains of mice) factors on acquisition of drug self-administration (IVSA protocol); 4) to characterize the effects of non-contingent drug pre-session administration on acquisition and extinction of drug self-administration.